The cooling effect in typical refrigeration systems is provided by the vaporization of liquid refrigerant in the cooling coils of a sealed evaporator. Comparatively large quantities of heat are absorbed as the liquid refrigerant is evaporated into vapor, and water or air can be cooled as it is passed over cooling coils that contain the evaporating refrigerant. Alternatively, refrigerant can be flooded into an evaporator that includes internal tubes through which water flows to be cooled. In either case, the refrigerant vapor is drawn from the evaporator by suction to a compressor, which increases the pressure and temperature of the vapor. The vapor is then pumped to a condenser where the latent heat of the pressurized vapor is removed, typically to the ambient air, condensing the refrigerant vapor back into a liquid. The condensed, pressurized liquid refrigerant is reintroduced into the evaporator through an expansion or metering device that reduces the pressure of the liquid refrigerant. The low pressure cold liquid refrigerant is again vaporized in the evaporator, and the above described cycle is repeated.
The pressure within a refrigeration system evaporator can reach unacceptably high values under a number of abnormal operating conditions. For example, chilled water systems pass water through evaporator cooling coils, and the chilled water is circulated to areas remote from the coils. For a variety of reasons, the refrigeration system and the water circulation system are often designed as separate systems. Through operating error, the refrigeration system can be shut down, but the water circulating pump left on. As the structure or system warms (because the refrigeration system is shut down), the temperature of the circulating water rises, causing warming within the evaporator and refrigerant evaporation, which in turn raises the pressure in the evaporator.
Leaking isolation valves on two pipe heating and cooling systems are another common source of evaporator over-pressure conditions. Two pipe heating and cooling systems use the same water and water circulation piping to both heat and cool a building. When the heating season arrives, isolation valves are closed, directing the circulated water from the refrigeration system to the heating system. Heated water can be inadvertently introduced into the refrigeration system evaporator if the isolation valves fail to properly close. The heated water (typically at about 180.degree. F.) will cause rapid vaporization of coolant within the evaporator, resulting in an evaporator over-pressure condition. Whatever the cause, evaporator over-pressure conditions, if allowed to persist, can ultimately cause damage to the evaporator.
Evaporators in conventional refrigeration systems are often provided with a relief valve that will vent refrigerant vapor to the atmosphere in response to the detection of an evaporator over-pressure situation. In many systems the relief means is a rupture disk designed to fracture at a specified pressure. Fracturing of the disk opens the evaporator to the atmosphere. While the venting of vapor to the atmosphere is an effective way to quickly reduce internal evaporator pressure, the vented refrigerant vapor is not recoverable, and replacement refrigerant must be added to the system after the over-pressure condition is stabilized. Refrigerant is an expensive commodity and in large systems several thousands of pounds can be lost from a system due to rupture disk venting. More importantly, many commonly used refrigerants have been shown to have an adverse effect on the environment when lost to the atmosphere. Finally, since refrigerant vapor is heavier than air and replaces oxygen in an enclosed space, the atmospheric venting of refrigerant in an enclosed space can result in injury or death to persons or animals occupying the space.
U.S. Pat. No. 4,332,136 discloses a refrigeration system that includes a buffer tank for receiving a limited amount of refrigerant vapor from an evaporator vapor chamber. While the pressure relief system disclosed by the '136 patent does not vent vapor to the atmosphere, the '136 system is designed only to provide a brief pressure decrease in an evaporator vapor chamber during loading peaks. The '136 system does not provide for non-atmospheric venting of evaporator over-pressure in system failure conditions, and, in fact, requires normal evaporator operation in order to accomplish its pressure buffering function.
It is an objective of the present invention to adequately deal with system threatening over-pressure conditions in the evaporator portion of refrigeration systems without releasing refrigerant vapor to the atmosphere.
It is another object of the present invention to provide for the unattended, safe removal of refrigerant from a refrigeration system in response to an evaporator over-pressure condition.
It is a further object of the present invention to provide for the automatic, unattended, de-energization of a refrigeration system in response to a detected evaporator over-pressure condition.
It is a feature of the present invention to provide a vessel for selectively storing liquid refrigerant vented from the evaporator component of a refrigeration system in response to a detected evaporator over-pressure condition.
It is a further feature of the present invention to provide a control system for automatically controlling valves for venting liquid refrigerant from the evaporator component of a refrigeration system in response to an over-pressure condition in the evaporator component of the system, and for selectively returning the vented liquid from the storage vessel to the refrigeration system after the over-pressure condition has been rectified.